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| Home > Publications database > Entwicklung planarer Ba$_{0,5}$Sr$_{0,5}$Co$_{0,8}$Fe$_{0,2}$O$_{3-δ}$ - Membranmodule zur Sauerstoffabtrennung und Analyse ihres Transportverhaltens |
| Book/Dissertation / PhD Thesis | FZJ-2015-03226 |
2015
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
Jülich
ISBN: 978-3-95806-044-9
Abstract: Oxygen transport membranes (OTMs) represent a promising alternative for the extraction of oxygen compared to energy intensive processes such as the cryogenic air separation. Especially ceramic, mixed ionic-electronic conducting membranes (MIECs) are of current interest. Due to their ability to transport oxygen via vacancies in the crystal lattice in case of sufficient high temperature and partial pressure gradients, such membranes can theoretically achieve a selectivity of 100% assuming the absence of any leakages. With respect to membrane material, mostly perovskites are used, showing high ionic and electronic conductance. In this context, the perovskite with the highest oxygen permeability is Ba$_{0,5}$Sr$_{0,5}$Co$_{0,8}$Fe$_{0,2}$O$_{3-\delta}$ (BSCF), which is also used in this work. Regarding the technical implementation, different design and operational concepts exist, whereas the respective oxygen transport is governed by a complex set of different mechanisms depending on each individual membrane system’s architecture. One part of this work addresses the modeling of the oxygen transport through a supported membrane. For this purpose, different approaches for individual transport mechanisms such as solid state diffusion, surface exchange, and transport in the support and gas phase are combined to one comprehensive model. With regard to the surface exchange, a correction factor is introduced, which takes into account the realistic topography of the membrane surfaces. This approach was verified by permeation measurements of supported samples with varying membrane layer thicknesses (8 - 400 $\mu$m), showing a good agreement between model and experiment. Characteristic values (porosity, tortuosity, spec. surface area) necessary for the modeling were determined using x-ray computed tomography. Overall the complete model allows the description of experimental data with a deviation of only 7%. Another focal point of this work is the development and testing of a complete ceramic membrane module. The manufacturing of planar compounds (20 mm diameter) consisting of membrane- (thickness 25 $\mu$m) and support-layers (thickness 1.4 mm) was done by sequential tape casting and lamination. Also, the adaption of the sintering program allows the fabrication of samples with a surface area of 110 x 110 cm$^{2}$, thus confirming the scalability of this manufacturing process. The compound’s outer surface is sealed by applying a ceramic layer. For this purpose, a BSCF-paste was developed and optimized with regard to a maximum green density, resulting in a gastight, crack-free layer with low porosity (ca. 5%). A gastight connection between BSCF-tube and compound was successfully achieved by garnishing and subsequent sintering under load. A tape-cast BSCF-foil (green thickness ca. 60 $\mu$m) is used as joining material, yielding a high mechanical stability and gas-tightness of the established connection. The membrane-module’s oxygen permeation was measured in 3-end mode undervarying conditions and is compared to reference samples. In this context, the results of the module, the reference samples and the developed transport model are consistent to each other. The viscous gas transport within the support layer was identified as the limiting factor. Thus future research and development needs to focus on the optimization of the support’s microstructure.
Keyword(s): Dissertation
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